Thermal expansion and superconductivity in alkali metal- and silver-doped Bi-Sr-Ca-Cu-O system

Samples with the nominal composition Bi2Sr2CaCu2Oy with Na doped at the Ca site and K doped at the Sr site are prepared by solid state reaction method. From the X-ray diffraction data it is found that all the samples have exhibited a single phase 2212. The D.C. electrical resistivity data show that for Na-doped samples the Tc (zero) varies from 80 K to 85 K and for K-doped samples it is from 79 K to 82 K. The loss of oxygen from these samples around 400degC was confirmed by high temperature dilatometry. The variation of the thermal expansion coefficient (''α'') with temperature for different alkali dopings are discussed. Also the samples with the nominal composition Bi4Sr3Ca3Cu4-xAgxOy (with x = 0, 0.1, 0.2, 0.3) were studied. (orig.)